Heart disease as referred to herein is caused by the formation of atherosclerotic lesions within coronary arteries. Atherosclerosis involves changes to the intima arterial vessel wall. Atherosclerosis is characterized by a progressive accumulation of plaque about the arterial wall and associated loss of elasticity. Artery walls consist of three layers: a layer of connective tissue, a second layer of smooth muscle cells and elastic connective tissue, and a third layer of endothelial cells. The endothelial cells are flattened and elongated and they overlap and are aligned in the direction of the blood flow. They have cell membrane surfaces which provide them with an “anti-stick” characteristic so as to avoid the build-up of substances on the inner surface of the blood vessel lumen.
Mechanical or chemical injury of the endothelial cells or damage to their non-stick surface provides sites for thrombocyte adhesion and leads to the formation of thrombi in the arterial wall. Some chemicals e.g. homocysteine and nicotine permanently open up the junctions between the endothelial cells perforating the endothelial layer. This damage allows monocytes (white blood cells) to stick to the formerly non-stick surface and pass into the intima itself, where they become active macrophages and scavenge oxidised LDL cholesterol. Aggregations of lipid-rich macrophages (known as foam cells) constitute early lesions which are often referred to as fatty streaks.
So called fatty streaks interfere with normal laminar blood flow, particularly at the site of blood vessel branches and bifurcations. They also continue to aggravate the surrounding tissue and provide sites for further thrombocyte adhesion. Over time, fatty streaks grow and connective tissue forms thereby progressively narrowing the lumen and consequently progressively restricting blood flow distally of the occlusion. Atherosclerosis may lead to myocardial infarction and angina pectoris and also contributes to the occurrences of strokes.
Currently, approximately 16 million U.S. citizens have diabetes and approximately 50% are unaware of their condition. Worldwide, approximately 110 million people suffer diabetes and recent projections suggest that this figure will have doubled in 10 years. The risk of heart disease and stroke is three to fives times greater for males with diabetes. Female diabetics are normally protected from heart disease until the menopause, however by the age of 55 they are seven times more likely to have heart disease than women without diabetes. Sixty five percent of people with diabetes also have high blood pressure and heart disease is the most common cause of death in patients with diabetes.
As a consequence of having diabetes, the blood vessel walls of a typical sufferer become thinned. If a balloon angioplasty procedure is indicated, this thinning of the walls presents two serious consequences. Firstly, since the vessel walls are thinner, they are mechanically weaker than healthy vessels and consequently they are more likely to rupture and sustain trauma. The second consequence of diabetes is that sufferers are more likely to suffer follow on post balloon angioplasty complications.
Studies by the US National Heart, Lung & Blood Institute comparing the effects of both balloon angioplasty and bypass procedures between groups of diabetic and non-diabetic and those patients with non-medication dependant diabetes indicates virtually identical long term outcomes, viz., a five year mortality rate of approximately 9%. Similar studies on medication dependant patients, i.e. those injecting insulin, indicated a five year mortality rate of 19% for post bypass surgery and 35% for post balloon angioplasty. Another interesting observation was that medication dependant diabetics are less likely to experience angina, the chest pain associated with oxygen deprivation through reduced blood flow.
On the basis of the preceding information it is evident that medication dependant diabetic patients fare considerably better when treated by bypass surgery than balloon angioplasty. Although there have been recent successes through employment of endoscopic coronary artery bypass graft (ECABG) techniques, bypass surgery typically involves sternotomy, and consequently considerable trauma, pain, and associated relatively long bed residence. Furthermore, although beating heart operations are becoming more common due to the employment of devices such as the Medtronic Endo Octopus™ stabilizer, many coronary artery bypass graft (CABG) techniques require the heart to be arrested. Amongst the possible complications encountered with CABG are the following:
Sternitis and mediastinitis, Haemolysis, Heparin rebound phenomena, Complement activation, Deterioration of the immune system, Poor appetite, Insomnia, Depression, Visual deficit, Memory deficit, Intellectual deficit, and Loss of sexual ability.
Thus, there is a need for a method by which the advantages of minimally invasive procedures and the long-term relative success rate of CABG can be combined. Such a method would be particularly suitable as a treatment for medication dependant diabetics.
The function of the methods and devices of the invention is to re-establish and maintain an adequate supply of oxygenated blood to heart tissue in areas formerly starved of oxygen. These regions of oxygen starved tissue are typically distal of an atherosclerotic lesion. The devices and methods described herein source oxygenated blood from a chamber of the heart, for example from the left ventricle (LV) and redirect this blood via a connecting conduit (shunt) to a portion of the left anterior descending coronary artery (LAD) or circumflex artery lying distal of the lesion.
U.S. Pat. No. 6,123,682 discloses a closed chest coronary bypass implant (conduit) for forming a channel directly from the left ventricle of the heart into a coronary artery distal to an obstruction or narrowing. In various embodiments disclosed, the implant can be used in an open-chest procedure, closed-chest procedure or alternatively, by catheter access to the coronary arterial vasculature and chambers of the heart via two incision sites, one in the groin and one in the right superior-anterior chest. The implant disclosed can be an L-shaped or T-shaped hollow stent which may be rigid or may have varying flexibilities. The device disclosed includes a capacitance pressure reservoir for storing pressurized blood during systole, for delivery to the heart muscles during diastole when pressures are reduced. In the catheter-controlled embodiment, a channel is ablated through both the chambers of the heart and the coronary artery wall using an ablating tip.
International Patent Specification No. WO 00/21461 discloses methods and devices for delivering a conduit into a heart wall to place a coronary vessel in communication with a heart chamber and for removing tissue from the vessel or heart wall to facilitate such communication.
WO 00/6607 discloses methods and devices for placing a conduit in fluid communication with a target vessel. The device includes a handle, a shaft assembly and a conduit having a vessel coupling.
WO 00/6609 also discloses methods and devices for forming a fistula device to place a target vessel in fluid communication with a source of blood, such as the aorta or a heart chamber.